Space discharge device



Aug. 9, 1932. H. D. BROWN ET AL.r SPACE DISCHARGE DEVI'CE sheets-sheet 1 Filed DeC. l5., 1926Y @wf W J; Y H. D. BI'ROWN ET AL SPACE DISCHARGE DEVICE Aug. 9, 193;.

Filed Dec.

l5, 1926 2 Sheets-Sheet H 2 WAZ/ lnverx'b of Herber: D. rown,

Cami! A. Subbclh,

Then Ab'bovney Patented Aug. 9, 1932 UNITED STATES APATENT orFicE c HERBERT D BROWN AND CAMIL AA.,SABBAH, OF SCHENEGTADY, NEW-YORK, ASSIGNORS l V or by the volatilization of mercury condensed in the upper part of the evacuated A object the T GENERAL ELECTRIC COMPANY,

A CORPORATION 0E NEW YORK srACE DISCHARGE DEVICE 'Appii'tion mea December 15, 1926, seriai No. i55,0'45.f

Our invention relates to space discharge devices comprising an anode arranged to transmit current in one direction through a circuit including a cathode, and has for its principal provision of anv improved anode structure whereby destructive arcs during the operation of such a device are prevented.

One of the most serious difficulties encountered in the operation of space'discharge def vices, such as a mercury rectifier, comprising a cathodey and oneV or more anodes, is the formation of destructive arcs either between a negatively charged anode and the 'cathode or between different anodes. Such arcs may 5 be caused by pockets of comparatively high vapor pressure produced within'the highly evacuated vessely at the surface of an anode, either by volatilization of the anodematerial which is vessel and drops or runs down on the hot surfaces of the anodes; i

' Volatilization of the'anode material is ob- `iectionable not only because of the destructive arcs which it tends to produce but also because of the fact that itl is' deposited as a conducting iilm onthe inner surfaces of the insulators interposed 'between the cathode and anodes. One'cause ofV overheating and' volatilization of the anodes'seems to be the' tendency of the current to concentrate at one spot on the anode surface. rThe reasons for this tendency are not well understood. It is known, however, that such concentration of 1"' the current can persist only as long as the affected spot is located in an. electrostatic field and has a higher conductivity and positive ion density than the remaining areas of the anode. In order to ensure proper current disl tribution over the active area of the anode we locate this area in a weak electrostatic field and give it such a contour that the stream of atoms, positive ions and electrons emanating '--1 from the concentration area will produce a rise in the conductivity of another part of the active area. Under these conditions a concentration of current at one spot of this active surface automatically increases the current at another spot on this surface and diverts the current from the affected spot to another part ofthe surface.l

ln, accordance with oury invention, these various diiiiculties are avoided by the provi' sion of an anode which is sol constructed that only its active surface is exposed to the interior of the evacuated chamber and that this surface is opposedto itself at dierent points andV located in avery weak electrostatic field.

. Our invention will be better understood from the following'idescription when `considered in connection with .the accompanying drawings and its scope will be pointed out in the appended'claims.

Referring tothe drawings,Fig. 1 shows a transversev section of a rectifier wherein our invention'has been embodied; Fig. 2 shows a section of an lanodeconstructed in accordance with our invention Figs. 3,4 and 5 show various detailsin a modified form. of anode; and Fig. `6y shows av further modification in the anode structure. H y

Fig. 1 shows a rectifier comprising an evacf uated vessell 1 whichis surrounded by a cool-4 ing chamber 2 and containsa mercury cathode 3, an anode connectedto a lead 4 and a starting electrode. 1t will be observed that the tank 1 is'insulated from the cathode 3 by meanscomprising an insulator 6, from the anode lead .4.by means ,comprising insulators 7 and'S, vand from the starting velectrode 5 by means comprising an insulator 9. Aside fromthe structure of the anode, the various illustrated features of the rectifier are well understood bythose skilled in the art and need not be described in furtherdetail.V Y 4 As shown more clearly by Fig. 2, the anode structure comprises a cylindrical anode 10 which is connectedat its upper end through a hollow stem 11 to the lead 4 and is welded at its lower end to a cylindrical member This member is provided with a liange 13 and is closed at itsupper end so as to forman annular chamber which surrounds the anode 10 andthe stem 11 and is interconnected with the interiorof this stem through ducts 14 in the upper end of the anode. Pipes l15 and 16 are arranged to permit the circulation of the electrostatic field at the active surface of the anode is substantially Zero, it is essential a cooling medium through the member 12 and the stem 11.

The member 12 is supported at the upper end of an extension 17 of the vessel 1 through means comprising the insulator 3 and a mem ber 18 provided with a flange 19 at its upper end and with a flange 2O at a point intermediate its ends. A sealed joint between the flange 2O and the upper end of the extension 1,7 is produced by means of a split ring 21 and bolts 22. The flanges 13 and 19 are clamped to the upper and lower suifaces of the insulator 8 by means comprising rings 23 and 24, bolts 25, a gasket 26 and the insulator 7. Under these conditions, vacuum tight seals are produced at the upper end of the extension 17 and at the upper and lower surfaces of the insulator 8.

.Y :In order to restrict the active area of the anode to a part of the surface located in a weak electrostatic field and to protect the interior surface of the insulator 8 from volatilized material which would tend to produce aconductive film on its inner surface, an in- 1. sulation shield 27 of alumina, or the like, is

suspendedfrom the insulator 8 in a manner to cover the part of the member 18 located within the vessel 1 and to cover the interior surface of the anode at its lower en-d. An insulation washer 28 and a funnel-shaped member 29 are supported upon the lower end of the member 18 and held in contact with the lower endof the shield 27 by suitable means shown as screws 30.

It `will be apparent that this .structure not only limits the active surface of the anode to an area where the electrostatic field is substantially zero and shields the insulator surface from the vaporized material of the anode, but'also .shields the hot surface of the anode from condensed mercury.

The length of the interior anode surface that should be covered by the insulation vshield 27 is Vdependent on the internal diA ameter of the anode. In order to ensure that that the insulation shield extend up into the anode a distance which is of the same order as the internal diameter of the electrode. Under these conditions the electrostatic lines of force produced at opposed points on the active surface tend to neutralize each other and the danger of concentration of current at one spot of the anode surface is avoided due both to the fact that any electrons emitted from the active surface of the anode are in a veryl weak electrostatic field and to the further fact that any stream of positive ions produced by thes-e electrons is projected into an opposed area of this surface thereby increasing the conductivity of this opposed areaand preventing further concentration of the current at theafl'ected spot. l Y

The anode structure illustrated by Figs. 3,

4 and 5 differs from that illustrated by Fig. 2 in that it comprises an anode 31 provide-d with a plurality of recesses 32 in its lower end and with cooling ducts 33 which are located between the recesses 32 and extend between the upper and lower ends of the anode. In order to confine the arc to a part of the anode surface where the electrostatic field is substantially zero, the insulation shield is extended up into the recesses 32 far enough to cover the part of thes'urface .where the electrostatic lines of flux do not neutralize each other.-

Fig. 6 shows an anode structure comprising an external anode 34 provid-ed with a flange 35 which is clamped between an insulator 36 and an insulator 37 in a manner to form a vacuum tight jointr at the lower surface of t-he flange. In this structure, an insulation shield 38 supported on the insulator 37 is arranged to extend into the anode chamber far enough to confine the arcto a part of the anode surface where the electrostatic field is substantially Zero and into the evacuated chamber far enough to protect the interior surface of the insulator 37 from volatilized anode material. The other details of this structure will be readily understood in view of what has been said with respect to the previous figures.

The embodiments of the invention illus-` tratedy and described herein have been selected for the purpose of clearly setting forth the principles involved. It will be apparent, however, that the invention is susceptible of being modified to meet the diierent conditions encountered in its use and we therefore aim to cover by the appended claims all modilications within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is-

1. A mercury arc device comprising yan evacuated vessel, a cathode, an anode having a recess formed therein and provided with an active surface and an inactive surface, said active surface and a portion of said inactive surface being formed byv they surfaces of said recess, and an insulation shield mounted within said vessel and extending into said recess of said anode a distance at least as great as the width of said recess to cover'said portion of said inactive surface within said recess.

2. A mercury arc device comprising an evacuated vessel, a cathode, a hollow insulator, an anode supported on said insulator and provided with a cylindrical recess in one of its surfaces, said anode being provided with an active surface and an inactive surface, said active surface and a portion of said inactive surface being formed by the walls of said recess, and an insulation shield extending into said recess a distance at least as great as thediameter of said recess tocover saidV portion of said inactive surface within said recess and extending over the interior surface of said hollow insulator.

Y 3. A mercury arc device comprising an evacuated vessel, a cathode, an anode having a cylindrical recessed surface and provided with an active surface and an inactive surface, said active surface and a portion of said inactive surface being formed by said cylindrical recessed surface of said anode, a hollow insulator interposed between said cathode and said anode, and an insulation shield mounted within said vessel to cover the interior surface of said insulator, said shield extending into said anode a distance at least as great as the internal diameter of said anode recess to cover said portion of said inactive surface within said anode.

In witness whereof, the said HERBERT D. BRowN has hereunto set his hand this 14th day of December, 1926, and the said CAMIL A. SABBAH has hereunto set his hand this 2nd day of December, 1926.

HERBERT D. BROWN. CAMIL A. SABBAH. 

